Nondestructive Readout Research Articles

Optimizing Ferroelectric and Interface Layers in HZO-Based FTJs for Neuromorphic Applications

Nonvolatile memories especially the ferroelectric (FE)-based ones such as ferroelectric tunnel junctions (FTJs) and ferroelectric field-effect transistors (FeFETs) have recently attracted a lot of attention. FTJs have been intensively researched for the last decade and found to be very promising memory devices due to their significant nondestructive readout advantage as compared to conventional ferroelectric random access memory (FRAM). However, more research is needed on FTJ devices to obtain reliable endurance and retention behavior. In this article, we demonstrate the characteristics and performance of zirconium-doped hafnium oxide-based FTJ devices in terms of FE switching and reliability. This is investigated for FTJ stack structure tuning as well as for the FE switching process in FTJ devices. The FTJ memory switching characteristics, the effects of polarization switching on the write conditions, and the impact of pulse width and pulse amplitude on switching are investigated. The impact of FE layer thickness and interface layer type/thickness are reported to obtain a maximum FTJ <inline-formula> <tex-math notation="LaTeX">${I}_{ \mathrm{\scriptscriptstyle ON}}/{I}_{ \mathrm{\scriptscriptstyle OFF}}$ </tex-math></inline-formula> ratio (memory window) and reliable performance. The maximum <inline-formula> <tex-math notation="LaTeX">${I}_{ \mathrm{\scriptscriptstyle ON}}/{I}_{ \mathrm{\scriptscriptstyle OFF}}$ </tex-math></inline-formula> ratio changes depending on the FE layer (zirconium-doped HfO₂ layer) thickness (12, 8, 6, and 4 nm), the interface layer type (SiO₂, Al₂O₃), and thickness (1 and 2 nm), indicating the maximum value of <inline-formula> <tex-math notation="LaTeX">${I}_{ \mathrm{\scriptscriptstyle ON}}/{I}_{ \mathrm{\scriptscriptstyle OFF}}$ </tex-math></inline-formula> ratio for a 1 nm SiO₂ interface layer stack. Moreover, a stable endurance of 10⁴ cycles is reported and extrapolated measurements suggest stable retention for more than ten years. Time-dependent breakdown analysis was performed to investigate the reliability of devices indicating a lifetime of ten years.

Numerical simulation of single-event effects in fully-depleted silicon-on-insulator HfO&lt;sub&gt;2&lt;/sub&gt;-based ferroelectric field-effect transistor memory cell

Ferroelectric field-effect transistor (FeFET) memory is currently a popular non-volatile memory. It has many advantages such as nonvolatility, better scalability, energy-efficient switching with non-destructive read-out and anti-radiation. To promote the application of FeFET in radiation environments, the single-event transient effect in HfO&lt;sub&gt;2&lt;/sub&gt;-based fully-depleted silicon-on-insulator (FDSOI) FeFET memory cell is studied by technology computer aided design (TCAD) numerical simulation. The effects of different incident positions and angles of heavy ions and the drain bias voltage on the characteristics of the memory cell are analyzed. The results show that the corresponding polarization state in the HfO&lt;sub&gt;2&lt;/sub&gt; ferroelectric layer will not reverse regardless of the change for the incident position of heavy ions, but the transient change of the output voltage for the memory cell will be affected. The most sensitive area is close to the drain-body junction area. Moreover, with the decrease of the ion incidence angle, the peak of output voltage for the memory cell increases. And the effect of the incident angle change is more obvious when reading data is “0” rather than “1”. The peak of output voltage for the memory cell is modulated by the drain bias voltage, and the modulation effect is more obvious when reading data is “1” rather than “0”. The above findings provide theoretical basis and guidance for the anti-single event design of the FDSOI FeFET memory cell.

Unsymmetrical benzothiazole-based dithienylethene photoswitches.

Herein, we investigate the structure-property relationships in a new series of benzothiazole based unsymmetrical hexafluorocyclopentene dithienylethenes (DTEs) and compare the results with the known facts for symmetric diarylethenes (DAEs). We reveal high photocyclization efficiency resulting from a significant shift of ground state equilibrium to the antiparallel conformation and a barrierless excited state pathway to conical intersection, which remains unperturbed even in polar solvents for most of the prepared DTEs. Furthermore, we uncover that the rate of back thermal cycloreversion correlates clearly more with the central C-C bond-length in the transition state than with the central C-C bond-length in the ground state of the cyclic form. Finally, our detailed vibrational spectral analysis of studied DTEs points out significant changes in Raman and infrared spectra during photoswitching cycles which pave the way for a non-destructive readout of stored information.

Electrolyte-Gated Vertical Synapse Array based on Van Der Waals Heterostructure for Parallel Computing.

Recently, three‐terminal synaptic devices, which separate read and write terminals, have attracted significant attention because they enable nondestructive read‐out and parallel‐access for updating synaptic weights. However, owing to their structural features, it is difficult to address the relatively high device density compared with two‐terminal synaptic devices. In this study, a vertical synaptic device featuring remotely controllable weight updates via e‐field‐dependent movement of mobile ions in the ion‐gel layer is developed. This synaptic device successfully demonstrates all essential synaptic characteristics, such as excitatory/inhibitory postsynaptic current (E/IPSC), paired‐pulse facilitation (PPF), and long‐term potentiation/depression (LTP/D) by electrical measurements, and exhibits competitive LTP/D characteristics with a dynamic range (G max/G min) of 31.3, and asymmetry (AS) of 8.56. The stability of the LTP/D characteristics is also verified through repeated measurements over 50 cycles; the relative standard deviations (RSDs) of G max/G min and AS are calculated as 1.65% and 0.25%, respectively. These excellent synaptic properties enable a recognition rate of ≈99% in the training and inference tasks for acoustic and emotional information patterns. This study is expected to be an important foundation for the realization of future parallel computing networks for energy‐efficient and high‐speed data processing.

Smart Readout of Nondestructive Image Sensors with Single Photon-Electron Sensitivity.

Image sensors with nondestructive charge readout provide single-photon or single-electron sensitivity, but at the cost of long readout times. We present a smart readout technique to allow the use of these sensors in visible light and other applications that require faster readout times. The method optimizes the readout noise and time by changing the number of times pixels are read out either statically, by defining an arbitrary number of regions of interest in the array, or dynamically, depending on the charge or energy of interest in the pixel. This technique is tested in a Skipper CCD showing that it is possible to obtain deep subelectron noise, and therefore, high resolution of quantized charge, while dynamically changing the readout noise of the sensor. These faster, low noise readout techniques show that the skipper CCD is a competitive technology even where other technologies such as electron multiplier charge coupled devices, silicon photo multipliers, etc. are currently used. This technique could allow skipper CCDs to benefit new astronomical instruments, quantum imaging, exoplanet search and study, and quantum metrology.

Optoelectronic Memory Capacitor Based on Manipulation of Ferroelectric Properties.

Here, we report on the fabrication of an optoelectronic memcapacitor (memory capacitor) by manipulation of ferroelectric properties through the ferroelectric-semiconductor interface based on a ZnO/PZT (Pb1.1(Zr0.52Ti0.48)O3) capacitor. A ZnO layer was deposited on PZT by the chemical vapor deposition method to achieve the memcapacitive effect. The capacitance-voltage and time-dependent capacitance characteristics of the Al/ZnO/PZT/Al memcapacitor were used as the main outcome measurement. In an asymmetric PZT structure with a ZnO layer, two stable states in the capacitance were obtained, which can be written by either optical or electrical pulses. In addition, the illuminated capacitive characters of the device showed a photovoltaic effect that is sensitive to wavelengths and can be used for nondestructive readout. Thus, this work proposes a low-cost structure solid-state memcapacitor exhibiting the promising potential for memory and computation applications with the ability to program and readout by electrical or optical signals.

Controlled manipulation of conductive ferroelectric domain walls and nanoscale domains in BiFeO3 thin films

Recently, there is a surge of research interest in configurable ferroelectric conductive domain walls which have been considered as possible fundamental building blocks for future electronic devices. In this work, by using piezoresponse force microscopy and conductive atomic force microscopy, we demonstrated the controlled manipulation of various conductive domain walls in epitaxial BiFeO3 thin films, e.g. neutral domain walls (NDW) and charged domain walls (CDWs). More interestingly, a specific type of nanoscale domains was also identified, which are surrounded by highly conductive circular CWDs. Similar nanoscale domains can also be controlled created and erasured by applying local field via conductive probe, which allow nondestructive current readout of different domain states with a large on/off resistance ratio up to 102. The results indicate the potential to design and develop high-density non-volatile ferroelectric memories by utilizing these programable conductive nanoscale domain walls.

Battery-Less Electronic Layer Detectors Array (ELDA) for In-Tool DUV Detection by FinFET CMOS Technology

An in-tool, on-wafer detectors’ array for monitoring deep ultraviolet (DUV) light is proposed and demonstrated in this work. The proposed electronic layer detectors array (ELDA) features FinFET CMOS compatibility and compact pixel structure. Its minimum pixel pitch can reach 0.7 $\mu \text{m}$ , enabling the realization of high spatial resolution array. Most importantly, the sensing results from DUV exposure can be stored in the in-pixel storage node for days without external power supply, providing offline electrical nondestructive measurement and readout.

Ferroelectricity in CMOS-Compatible Hafnium Oxides: Reviving the ferroelectric field-effect transistor technology

A Ferroelectric Field-Effect Transistor (FEFET) is a promising candidate for next-generation memory devices because it offers numerous advantages, such as its high speed, low energy profile, and nondestructive readout process. FEFETs merge logic and memory functionality in a single device, allowing efficient data transfer and a high packing density, which could make them vital for use in future in-memory computing architectures. Although issues related to the integration of perovskite materials in the state-of-the art semiconductor industry limited their commercial success, the discovery of ferroelectricity in CMOS-compatible doped hafnium oxides led to a re-emergence of FEFETs in advanced microelectronics. The demonstration of ferroelectricity in doped hafnia at extremely thin film thicknesses plus its low permittivity, high coercive field (Ec), environment-friendly composition, and excellent CMOS compatibility are expected to unleash the promise of FEFETs, and significant progress has been made in this regard.

Effect of ferroelectric and interface films on the tunneling electroresistance of the Al2O3/Hf0.5Zr0.5O2 based ferroelectric tunnel junctions

Ferroelectric random-access memory (FRAM) based on conventional ferroelectric materials is a non-volatile memory with fast read/write operations, high endurance, and 10 years of data retention time. However, it suffers from destructive read-out operation and lack of CMOS compatibility. HfO2-based ferroelectric tunnel junctions (FTJ) may compensate for the shortcomings of FRAM by its CMOS compatibility, fast operation speed, and non-destructive readout operation. In this study, we investigate the effect of ferroelectric and interface film thickness on the tunneling electroresistance or ON/OFF current ratio of the Hf0.5Zr0.5O2/Al2O3 based FTJ device. Integrating a thick ferroelectric layer (i.e. 12 nm Hf0.5Zr0.5O2) with a thin interface layer (i.e. 1 nm Al2O3) resulted in an ON/OFF current ratio of 78. Furthermore, to elucidate the relationship between ON/OFF current ratio and interfacial properties, the Hf0.5Zr0.5O2-Al2O3 films and Ge-Al2O3 interfaces are examined via time-of-flight secondary ion mass spectrometry depth profiling mode. A bilayer oxide heterostructure (Hf0.5Zr0.5O2/Al2O3) is deposited by atomic layer deposition (ALD) on the Ge substrate. The ON/OFF current ratio is enhanced by an order of magnitude when the Hf0.5Zr0.5O2 film deposition mode is changed from exposure (H2O) ALD to sequential plasma (sequential O2–H2) ALD. Moreover, the interfacial engineering approach based on the in situ ALD H2-plasma surface pre-treatment of Ge increases the ON/OFF current ratio from 9 to 38 by reducing the interfacial trap density state at the Ge-Al2O3 interface and producing Al2O3 with fewer oxygen vacancies as compared to the wet etch (HF + H2O rinse) treatment of the Ge substrate. This study provides evidence of strong coupling between Hf0.5Zr0.5O2 and Al2O3 films in controlling the ON/OFF current ratio of the FTJ.

Photo-Switchable Aggregation-Induced Emission of Bisthienylethene-Dipyrimido[2,1-b][1,3]benzothiazole Triad.

A bisthienylethene-dipyrimido[2,1-b][1,3]benzothiazole (BTE-2PBT) triad has been designed and synthesized based on our recent discovery of PBTs as atypical propeller-shaped novel AIEgens. The triad not only maintains the photochromic properties of BTE moiety in solution, film, and solid state but also exhibits remarkable AIE properties. Moreover, the fluorescence of BTE-2PBT PMMA film could be modulated with high contrast by alternate UV and visible light irradiation. Photoerasing, rewriting, and non-destructive readout of fluorescent images on BTE-2PBT PMMA film well demonstrate its potential application as optical memory media.

Fully Planar Impact Ionization (I 2)-RAM Cell With High-Performance and Nondestructive Readout

This work presents a fully planar, nondestructive readout, and high-performance impact ionization random access memory (I <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> 2</sup> -RAM) cell having static random access memory (SRAM) characteristics. The proposed memory cell consists of a bipolar I <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> MOSFET (BIMOS) whose source region is shared with the drain region of a control gate (CG)-nMOS. The proposed I <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> -RAM offers excellent static characteristics, including write “1” (W1) time of ~0.5 ns, superior nondestructive readout time of ~0.4 ns, and sense margin (SM) of ~242 μA/μm at room temperature (300 K). The proposed I <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> -RAM cell also shows a static retention time (RT) >3600 s at a lower supply voltage of V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS</sub> = 1.1 V for 300 K and 358 K temperatures. It additionally has a high read current ratio of ~ 2×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sup> and ~ 4×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> at temperatures 300 and 358 K, respectively. The proposed I <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> -RAM cell is promising candidate for embedded-RAM and high-performance applications.

Entanglement transport and a nanophotonic interface for atoms in optical tweezers.

The realization of an efficient quantum optical interface for multi-qubit systems is an outstanding challenge in science and engineering. Using two atoms in individually controlled optical tweezers coupled to a nanofabricated photonic crystal cavity, we demonstrate entanglement generation, fast nondestructive readout, and full quantum control of atomic qubits. The entangled state is verified in free space after being transported away from the cavity by encoding the qubits into long-lived states and using dynamical decoupling. Our approach bridges quantum operations at an optical link and in free space with a coherent one-way transport, potentially enabling an integrated optical interface for atomic quantum processors.

Measuring perceived sweetness by monitoring sorbitol concentration in apples using a non-destructive polarization-based readout.

The determination and qualification of sugars in fruits are important for quality control and assurance of horticultural produce. The sugars determine the sweetness levels in fruits. The requirement for a universal technique that is also robust to predict the sweetness of the fruit in a non-destructive fashion is immense. The handheld refractometer, hydrometer, electronic tongues, and high-pressure liquid chromatography (HPLC) in combination with other detectors have long been used to determine the sweetness of horticultural produce. Though these techniques are very accurate and useful, they require extensive sample preparation and are generally time-consuming and expensive. Optical techniques like visible to near-infrared spectroscopy (vis/NIRS) are simple in use and can rapidly predict the sweetness of the fruit in a non-destructive fashion. The instrumentation used in these techniques is simple and cost-effective for routine analysis of the fruits. However, their systems need calibration for each sample, and the measurement variation depends on the type of horticultural produce on which measurements are done. An optical-based technique is proposed that uses reflected phase information of the incident light and correlates the same to the presence of sorbitol concentration in apples. The refractive index of sorbitol varies as the fruit ripens due to its change in concentration, and the reflected phase information accordingly changes. Monitoring the reflected phase information allows a prediction mechanism of the sweetness content in the fruit.

Significantly Photo‐Thermochromic KNN‐Based “Smart Window” for Sustainable Optical Data Storage and Anti‐Counterfeiting

AbstractFerroelectric photo‐thermochromic (PTC) materials with both high coloration contrast and high transparency have attracted great attention for their applications in “smart window” for non‐contact optical information storage. Nevertheless, it has been challenging to develop a ferroelectric PTC material that simultaneously meets the distinct transparency and coloration contrast requirements. Herein, dual rare‐earth ions doping of 1%Er‐(K0.5Na0.5)0.985La0.015NbO6(Er‐KNLN) ferroelectric ceramics is aimed at increasing the optical transmittance and obtaining an ideal coloration contrast. The traditional solid‐state reaction is exploited for ceramics fabrication, and the optimal optical transmittance (≈70% at 900 nm) can be obtained due to finer grains, more symmetrical structure, and compact structure in samples sintered at a suitable temperature (such as ≤1165 °C). Contributed from the trapping and de‐trapping of charge carriers in vacancy‐related defects, the Er‐KNLN ceramics exhibit obvious PTC behavior and the novel impedance modulation is developed. The coupling between PTC behavior and optical transparency, lanthanide up‐conversion emission, patterned display, and room temperature impedance enables nondestructive rewritable and readout characteristics of multi‐mode “0” and “1” states. This work solves the main problems hampering the promising applications of ferroelectric materials and paves a way for developing multifunctional optical memory smart windows.

Size-Controlled Polarization Retention and Wall Current in Lithium Niobate Single-Crystal Memories.

Highly conductive domain walls in insulating ferroelectric LiNbO3 (LNO) single-crystal thin films with atomic smoothness are attractive for use in high-density integration of the ferroelectric domain wall random access memory (DWRAM) because of their excellent reliability and high read currents. However, downscaling of the memory size to the nanoscale could cause poor polarization retention. Understanding the size-dependent electrical performance of a memory cell is therefore crucial. In this work, highly insulating X-cut LNO thin films were bonded to SiO2/Si wafers and lateral mesa-like cells were fabricated on the film surfaces, where contact occurred with two-sided electrodes along the polar z-axis. Under application of an in-plane electric field above a coercive field (Ec), the domain within each memory cell was switched to be antiparallel to the unswitched referencing domain at the bottom; this resulted in the formation of a conducting domain wall, which enables the nondestructive readout strategy of the DWRAM. The cell, which has a lateral length (l) above a critical size (l0) of 105 nm, is found to be a mixture of two phases across the cell area. The inner area of the cell suffers from poor polarization retention because Ec = 150 kV/cm, as demonstrated by in-plane piezoresponse force microscopy imaging. In comparison, the outer periphery domains, which have lengths of 70 nm (∼l0/2), show good retention but require a much higher Ec of 785 kV/cm. The relevant physics is discussed as phase reconstruction occurs after release of the in-plane compressive strain near the outer regions; the results show good agreement with those of one-dimensional thermodynamic calculations and phase-field simulations. The measured current-voltage curves demonstrated a sudden enhancement of the wall current across the cell when l < l0, thus implying higher readout wall currents and better retention for the DWRAM at higher storage densities.

Constructing photochromic diarylethene with NIR-absorption beyond 800 nm

Near-infrared (NIR) absorbing dyes have received increasing attention due to their ability of NIR radiation absorption and efficient light-to-heat conversion. NIR absorbing photochromic diarylethene (DAE) materials, which could modulate NIR absorption upon light stimulation, provide a convenient route to fabricate smart NIR absorbers. In this study, we constructed a new NIR absorbing photochromic DAE system, of which NIR absorption stems from closed isomer bearing triarylamine (TAA) radical (TDEc-ox). Upon 365/440 nm light irradiation, the open isomer TDEo undergoes photo-oxidation and cyclization to yield TDEc-ox, which exhibited NIR absorption at 928 nm in chloroform. TDEc-ox possesses a photo-inactive feature facilitating non-destructive readout of NIR absorption and high stability (lifetime time ≥ 3 days). Contrary to TDEo, the closed isomer TDEc cannot be directly photo-oxidized to give TDEc-ox. This discrepancy makes TDEc a “photogenerated TAA radical reservoir”: after cycles of photoisomerization, a controllable accumulation of NIR absorbing TDEc-ox can be achieved.

Mapping Cell Viability Quantitatively and Independently From Cell Density in 3D Gels Noninvasively.

In biomanufacturing there is a need for quantitative methods to map cell viability and density inside 3D bioreactors to assess health and proliferation over time. Recently, noninvasive MRI readouts of cell density have been achieved. However, the ratio of live to dead cells was not varied. Herein we present an approach for measuring the viability of cells embedded in a hydrogel independently from cell density to map cell number and health. Independent quantification of cell viability and density was achieved by calibrating the 1H magnetization transfer- (MT) and diffusion-weighted NMR signals to samples of known cell density and viability using a multivariate approach. Maps of cell viability and density were generated by weighting NMR images by these parameters post-calibration. Using this method, the limits of detection (LODs) of total cell density and viable cell density were found to be 3.88 ×108 cells · mL -1· Hz -1/2 and 2.36 ×109 viable cells · mL -1· Hz -1/2 respectively. This mapping technique provides a noninvasive means of visualizing cell viability and number density within optically opaque bioreactors. We anticipate that such nondestructive readouts will provide valuable feedback for monitoring and controlling cell populations in bioreactors.

Compact Superconducting Lookup Table Composed of Two-Dimensional Memory Cell Array Reconfigured by External DC Control Currents

We investigated the hardware implementation of an area-efficient superconducting lookup table (LUT) based on a single flux quantum (SFQ) logic by using a newly proposed small memory cell. The memory cell is composed of a nondestructive read-out (NDRO) flip-flop with input circuits that convert the input dc current to an SFQ pulse signal. The datum can be written to the selected memory cell in the 2-D memory cell array by applying both <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> - and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> -directional dc control currents. The data stored in the memory cell array can be reset simultaneously by applying a dc current to a common reset line. By employing the new memory cell, wiring for reconfiguring the data and resetting the memory cell array can be drastically simplified compared to that of the conventional SFQ LUT. We implemented and tested the memory cell and confirmed the correct operation with wide dc bias and input-current margins. We designed the 16-b LUT using the designed memory cells. The circuit area and the number of Josephson junctions of the 16-b LUT is reduced by approximately 24 and 41%, respectively, compared to those of the LUT based on the conventional architecture. We experimentally obtained the correct operation and reconfiguration of the 4-b LUT that uses the new memory cells with a normalized bias margin of –22 to +7%.

Two-dimensional ferroelectric channel transistors integrating ultra-fast memory and neural computing

With the advent of the big data era, applications are more data-centric and energy efficiency issues caused by frequent data interactions, due to the physical separation of memory and computing, will become increasingly severe. Emerging technologies have been proposed to perform analog computing with memory to address the dilemma. Ferroelectric memory has become a promising technology due to field-driven fast switching and non-destructive readout, but endurance and miniaturization are limited. Here, we demonstrate the α-In2Se3 ferroelectric semiconductor channel device that integrates non-volatile memory and neural computation functions. Remarkable performance includes ultra-fast write speed of 40 ns, improved endurance through the internal electric field, flexible adjustment of neural plasticity, ultra-low energy consumption of 234/40 fJ per event for excitation/inhibition, and thermally modulated 94.74% high-precision iris recognition classification simulation. This prototypical demonstration lays the foundation for an integrated memory computing system with high density and energy efficiency.